1. Field of the Invention
The application relates to a method and a related communication device used in a wireless communication system and related communication device, and more particularly, to a method of handling emergency session and a related communication device in a wireless communication system.
2. Description of the Prior Art
A GSM (global system for mobile communication) system, initiated by the third generation partnership project (3GPP), is now being regarded as anew radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the GSM system, an UMTS (universal mobile telecommunication system) includes a plurality of base stations and communicates with a plurality of mobile stations (MSs), also referred as to user equipments (UEs).
A General packet radio service (GPRS) is a packet oriented mobile data service on GSM cellular communication systems. GPRS enhances the second generation (2G) phones to enable them to send and receive data more rapidly. With a GPRS connection, the phone is “always on” and can transfer data immediately, and at higher speeds: typically 32-48 kbps. An additional benefit is that data can be transferred at the same time as making a voice call. GPRS is now available on most new phones.
GPRS is part of a series of technologies that are designed to move the 2G networks closer to the performance of 3G (the third generation) networks. The key characteristic of a 3G network is its ability to transfer large amounts of data at high speed (up to 2 Mbps), enabling applications like video calling, video downloads, web browsing, email, etc. By increasing the speed of a 2G network, some of these applications become possible, e.g. web browsing and sending or receiving emails with large attachments.
A GPRS detach procedure is used in the following conditions: (1) to detach the IMSI for GPRS services only. Independent of the network operation mode, this procedure is used by all kind of GPRS MSs; (2) as a combined GPRS detach procedure used by GPRS MSs operating in MS operation mode A or B to detach the IMSI for GPRS and non-GPRS services or for non-GPRS services only, if the network operates in network operation mode I and no circuit-switched transaction is ongoing; (3) in the case of a network failure condition to indicate to the MS that a re-attach with successive activation of previously active PDP contexts shall be performed. In this case, the MS may also perform the procedures needed in order to activate any previously active multicast service(s); or (4) to detach the IMSI or IMEI for emergency bearer services.
IP multimedia subsystem (IMS) emergency calls are supported in the specification and the UE may initiate an IMS emergency call on the packet switch (PS) domain if the network supports the IMS emergency call service. An indication is provided to inform the UE that IMS emergency call services are supported. A UE will perform the GPRS detach procedure and detach itself from the network on sending DETACH REQUEST message when the SIM is removed from the device. The SIM contact to the device can be lost due to some mechanical problem e.g. loose SIM contact or user drop the phone while in a call. In this case, the UE will detach the device from the PS service even when PS emergency session e.g. IMS emergency call was active. As a result the emergency call will be dropped and it may take some time to make another emergency call after user properly put the SIM card back in the device. In some time critical case this delay is quite significant.